Permanent magnets configuring a component of a motor are used in a variety of configurations as shown below, in accordance with applications and specifications. The configurations include, for example, a rotor formed with permanent magnets that are secured on the surface of a rotor core thereof, and a rotor formed with permanent magnets of a predetermined shape that are arranged and secured to the inside of a rotor core thereof. With the configurations, the permanent magnets to be secured are selected from a variety of materials, such as sintered magnets and bonded magnets, having different magnetic properties depending on required motor performances. Moreover, the permanent magnets employ various types of shapes, such as circular-arc imbricate magnets, plate-like magnets, and ring magnets.
Moreover, permanent magnets are used in a wide range of applications including a type of motor in which permanent magnets are secured to a bracket side thereof and a rotor is rotated utilizing a magnetic field generated by the permanent magnets.
Conventionally, the permanent magnets of this kind are secured to the rotor core or the bracket, chiefly by bonding process using adhesive.
Hereinafter, the aforementioned bonding process is briefly described with reference to FIGS. 5A and 5B.
FIG. 5A is a plan view illustrating the bonding process of a conventional rotor. FIG. 5B is a cross-sectional view illustrating the bonding process of the conventional rotor.
First, as shown in FIGS. 5A and 5B, adhesive 22 is charged between adherend materials, such as magnet pieces 23 and rotor core 21. Then, charged adhesive 22 is cured to bond and secure rotor core 21 and magnet pieces 23 by the bonding process including, for example, thermal curing, anaerobic curing by purging air, and ultraviolet-light irradiation curing, used alone or in combination with them depending on curing characteristics of adhesive 22.
On the other hand, when using permanent magnets in an environment where adhesive cannot be used, a process without using adhesive is chosen, such as securing with a blade spring.
Moreover, it is possible to employ a process of press fitting described below, for a motor of an outer-rotor type in the case where a permanent magnet is secured to the inner peripheral side of a member such as a rotor core. In this case, first, when using a bonded magnet as the permanent magnet, the bonded magnet is pressed into a rotor frame, with the outside diameter of the bonded magnet being larger, by a predetermined dimension, than the inside diameter of the rotor frame to which the magnet is secured. Then, the bonded magnet is secured to the inside of the rotor frame utilizing elastic force of the bonded magnet, thereby configuring the rotor.
Furthermore, for a method of manufacturing another rotor, a process is disclosed in Patent Literature 1, for example. That is, the process described in Patent Literature 1 is such that a permanent magnet formed in a ring shape is secured to another ring member by pressing the outer periphery of the permanent magnet into the ring member. In this process, high bonding strength appears to be not necessary because, when the rotor rotates, the permanent magnet is pressed against the ring member by centrifugal force toward its outside, and because the permanent magnet is of a ring shape. For this reason, the method of bonding the permanent magnet is not particularly described in Patent Literature 1.
On the other hand, in the case where the bonded magnet is secured onto the surface of a rotor core, the method of bonding is such that the bonded magnet is secured onto the rotor core by press fitting process, utilizing a difference in dimension between the bonded magnet and the rotor core described above. This requires that the outside diameter of the rotor core be designed to be larger than the inside diameter of the ring-shaped bonded magnet. In this case, the press fitting is carried out in such a way that the ring-shaped bonded magnet is expanded in the radial direction, which results in an expansion of the bonded magnet in excess of its limit during press fitting. As a result, there has been a practical problem, e.g. a fracture of the bonded magnet in manufacturing, and a decrease in fracture strength of the bonded magnet.
Moreover, in the method of manufacturing the conventional rotor, when magnet pieces are secured to the rotor core and the edge portions of the circular-arc magnet pieces are joined to each other to form a ring-shaped bonded magnet, the shape of the respective magnet pieces changes as they cure. For this reason, there has been another problem that dimension accuracy of the rotor is less stable.
Furthermore, in forming the conventional rotor, there has been still another problem that, when forming the rotor, it is difficult to carry out precise phase-alignment between magnetizing positions of main magnet pieces and a magnetizing position of a magnet piece for positioning.
In addition, in the bonding process, there exist problems particular to adhesive, for example, variations in accuracy of bonding positions of the respective magnet pieces, eccentricities due to a bonding misalignment, and variations in outside diameters caused by variations in bonding thickness. As a result, there has been a problem that it is difficult to form the rotor with high accuracy. Additionally, high bonding strength has been necessary to prevent the respective magnet pieces from being scattered by centrifugal force when the rotor rotates.
Patent Literature 1: Japanese Patent Unexamined Publication No. H02-260402